outlook

As the first half of January comes into better focus, it appears that the blocking pattern over the Atlantic which has allowed the eastern half of the U.S. to be so cold in December will be making a comeback for a good part of January, which means another round of cold weather (but perhaps not as cold as December in the eastern half of the U.S.).

The forecast made by me (and made similarly by many others before December) argues for a more typical La Niña January, which calls for above normal temperatures through most of the country. However, typical La Niñas do not feature a large blocking pattern over the Atlantic, which prevents storms from progressing eastwards over the Atlantic Ocean. Instead, these storm systems retrograde, or move westwards, across Canada. The result is a greater northwesterly flow across North America, which, coupled with cold air from Siberia and western Canada, brings deep cold all the way down into the Southeast U.S. Conversely, the flow of maritime air from the Atlantic into eastern Canada results in above normal temperatures in that region.

What will be different this time around is the weather pattern in the West, which favors more storm systems digging southward along the West Coast as opposed to diving in west of the Rockies. The result will draw the below normal temperatures into most of the West as the upper-level energy travels across the southern U.S. The flow coming out of the mid-continent will suppress these storms and keep them further south than what would normally happen if there was no blocking pattern. Should the blocking pattern relax, these storm systems would be able to run northeast in the eastern U.S., which would bring the return of near normal to above normal temperatures to the East.

The result of the January weather pattern would be below normal temperatures for nearly the whole U.S., but the cold will at least be less dramatic in the eastern U.S. as was seen in December, which had a much more meridional flow with above normal temperatures in the western U.S.

If we were to keep this blocking pattern for most of January, this is what we could be looking at with respect to temperature:

Did I just say the Southeast had warmer AND colder risks? I most certainly did. Why? Because with more storm systems digging into the West, we could see them lift north more quickly as they work into the Southeast. This goes for the Mid-Atlantic as well. Conversely, if the blocking pattern we get is stronger than expected, the deep cold would be able to work farther into the Southeast.